1. Field of the Invention
The field of invention relates to asphalt binder and emulsion compositions. More specifically, the field relates to sulfur-extended asphalt binders (SEABs) and sulfur-extended asphalt binder emulsions (SEABEs).
2. Description of the Related Art
During the manufacturing and processing of materials containing asphalt such as asphalt-coated aggregates and hot asphalt mixes, working temperatures above 300° F. can cause problems for workers and their equipment. At temperatures greater than 300° F., sulfur and sulfur compounds present in asphalt or bitumen mix, such as elemental sulfur and naturally present heterorganic compounds, typically begin to react with other constituents in the asphalt and with the air. One of the main products of the sulfur reactions is hydrogen sulfide gas. Hydrogen sulfide in low quantities is an irritant, but in high quantities is toxic to humans. Similarly, heated sulfur that oxidizes in air forms sulfur dioxide, which has a noxious odor and is an air pollutant.
Sulfur, especially “free” or “elemental” sulfur, is an abundant and inexpensive material. Elemental sulfur is a byproduct of non-sweet natural gas and petroleum processing. Sources of free sulfur include petroleum refineries and gas sweetening plants. Because of the quantity of sulfur extracted from natural gas and petroleum, many sulfur producers consider elemental sulfur a waste product.
Others have attempted to use waste sulfur as an expander or filler for asphalt binders, but only with limited success. These efforts have only been successful in incorporating a small amount of sulfur into the asphalt binder, typically only up to a few percent of the total composition.
Those skilled in the art understand that sulfur forms hydrogen sulfide (H2S) gas, which is toxic to humans, starting at around 305° F. At and above that temperature, free sulfur in hydrocarbon environments dehydrogenates hydrocarbons and forms hydrogen sulfide. Heating sulfur to high temperatures in the presence of oxygen forms sulfur dioxide, which is noxious to humans and is an air pollutant. It is desirable to find a combination of asphalt materials that are workable at temperatures below 300° F. for worker comfort and safety as well as being more to the environment.
It is also desirable to find commercial uses for elemental sulfur. Incorporating sulfur into commercial products can transform what many consider a potential “waste” product into a product that has practical value.